Materials and methods are presented to deliver liquids to the interior of the eye, in a timed release, to treat ocular diseases and conditions. Formulations for liposomes as vehicles for substances to coat contact lenses are described.
Currently, eye drops, applied externally, are used as a method to treat internal ocular disorders. However, this method suffers from the disadvantage that the liquid has to pass through many ocular bathers, many of which have opposite properties. For example; the epithelial layer of the cornea allows hydrophobic drugs to pass, whereas the stroma (the next layer) allows hydrophilic drugs to pass, not hydrophobic. In addition, lacrimation and impermeability through the corneal epithelium are responsible for poor ocular bioavailability.
Ocular diseases and conditions include age related macular degeneration (AMD), a common, chronic degenerative condition of the macula, which is a part of the retina. AMD is characterized by loss of central vision, whereas peripheral vision remains unaffected. Growth and leakage of new blood vessels beneath the retina cause permanent damage to the light-sensitive retinal cells which then die off and create blind spots in the central vision. Treatment options for AMD include intravitreal injection of steroids and macromolecules (direct injection of the drugs into the vitreous humor), a very unpleasant technique that requires multiple applications. Complications include: endophthalmitis (an inflammatory condition of the intraocular cavities), increased IOP (intraocular pressure), retinal detachment, and development of glaucoma and cataracts. Other ocular conditions that require treatment are cataracts and infections. Treatments would benefit from timed release systems.
Liposomes are a possible choice for sustained release ocular drug delivery because of their amphiphilic nature. But, the conventional liposomal formulations have several disadvantages. The first major problem is the stability and low shelf life. These can be attributed to the fact that the phospholipids which form these liposomes are highly prone to oxidation and hydrolysis. Also liposomes have a tendency to fuse together, increasing the particle size and further cause light scattering.
Another major problem with the liposomes is the encapsulation efficiency. This depends on the concentration of cholesterol used to stabilize the phospholipid bilayers. High concentration of cholesterol leads to very inflexible bilayers leading to very low encapsulation and very slow release. On the other hand, low concentration of cholesterol causes very high encapsulation but very fast release. So, in order to overcome these disadvantages, there is a need to engineer the liposomal formulations to have higher stability, very low drug leakage, high encapsulation and slow release of the drug. Currently, there are no groups that have been successful in obtaining a protein drug release over 40 days.